A biochemical study will be made of the lysosomal metabolism of N-acetyl-D-(6-3H)glucosamine-labeled asialo-orosomucoid by the perfused rat liver. These investigations will include: (1) the determination of the kinetics of the glycoprotein (or its degradation products) being taken up and released by both the microsomal fraction (pinocytic vesicles) and the lysosomes; (2) a lysosomal fraction that has taken up glycoprotein will be isolated and incubated in vitro under isotonic conditions to maintain the membrane of the organelles intact in order to measure the rate of formatton of (3H)G1cNAc within the lysosomes and to show its release from the organelles into the medium; and (3) the same studies (1) and (2) will be repeated after pretreating the liver with leupeptin, an inhibitor that is known to slow down lysosomal proteolysis. In this way we will determine what relationships exist between peptide and carbohydrate digestion that is occurring on the same glycoprotein molecules.